Circulating IL-6 concentrations and abdominal adipocyte isoproterenol-stimulated lipolysis in women

Objective: To examine the association of plasma interleukin‐6 (IL‐6) concentrations with adiposity and fat cell metabolism in women. Methods and Procedures: Omental (OM) and subcutaneous (SC) adipose tissue samples were obtained from 48 healthy women (age: 47 ± 5 years, BMI: 26.9 ± 5.3 kg/m²) undergoing gynecological surgeries. Total and visceral adiposity were assessed by dual‐energy X‐ray absorptiometry and computed tomography, respectively. Measures of adipocyte lipolysis (basal, isoproterenol‐, forskolin‐, and cyclic dibutyryl‐adenosine monophosphate (AMP)‐stimulated) and adipose tissue lipoprotein lipase (LPL) activity were obtained. Plasma IL‐6 was measured by radioimmunoassay. Results: Plasma IL‐6 was positively correlated with total body fat mass (r = 0.32, P < 0.05), SC adipose tissue area (r = 0.35, P < 0.05), SC adipocyte diameter (r = 0.30, P < 0.05), and a trend was observed with visceral adipose tissue area (r = 0.20, P < 0.07). Plasma IL‐6 was positively correlated with glycerol released in response to isoproterenol (10^?5 to 10^?8 mol/l) by isolated SC (0.31 ≤ r ≤ 0.65, P < 0.05) and OM (0.36 ≤ r ≤ 0.40, P < 0.02) adipocytes, independent of menopausal status. No correlation was found with LPL activity. A subsample of women with high plasma IL‐6 (n = 10) was matched with women with low plasma IL‐6 (n = 10) for total body fat mass. OM adipocyte glycerol release in response to isoproterenol (10^?5 to 10^?8 mol/l) was higher in the subsample of women with elevated plasma IL‐6 (P ≤ 0.07). Discussion: We observed that OM lipolysis was significantly higher in women with elevated plasma IL‐6 for a similar body fat mass and menopausal status. These results suggest that higher circulating IL‐6 concentrations are associated with increased isoproterenol‐stimulated lipolysis especially in OM abdominal adipocytes in women.     

Subcutaneous Fat Shows Higher Thyroid Hormone Receptor‐α1 Gene Expression Than Omental Fat

The aims of this work were to evaluate thyroid hormone receptor‐α (TRα), TRα1, and TRα2 mRNA gene expression and TRα1:TRα2 ratio, identified as candidate factors for explaining regional differences between human adipose tissue depots. TRα, TRα1, and TRα2 mRNA levels, and the gene expressions of arginine–serine‐rich, splicing factor 2 (SF2), heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1), heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), and Spot 14 (S14) were evaluated in 76 paired adipose tissue samples obtained from a population of 38 women who varied widely in terms of obesity and body fat distribution. Gene expression for these factors was also studied in stromal‐vascular cells (SVCs) and mature adipocytes (MAs) from eight paired fat depots. TRα gene and TRα1 mRNA expression were increased 1.46‐fold (P = 0.006) and 1.80‐fold (P < 0.0001), respectively, in subcutaneous (SC) vs. visceral fat. These differences in gene expression levels were most significant in the obese group, in which the TRα1:TRα2 ratio was 2.24‐fold (P < 0.0001) higher in SC vs. visceral fat. S14 gene expression was also increased by 2.42‐fold (P < 0.0001) and correlated significantly with TRα and TRα1 gene expression and with the TRα1:TRα2 ratio. In agreement with these findings, hnRNP A1:SF2 ratio was decreased by 1.39‐fold (P = 0.001). TRα and S14 levels were 2.1‐fold (P < 0.0001) and 112.4‐fold (P < 0.0001), respectively, higher in MAs than in SVCs from both fat depots. In summary, genes for TR‐α, their upstream regulators, and downstream effectors were differentially expressed in SC vs. omental (OM) adipose tissue. Our findings suggest that TRα1 could contribute to SC adipose tissue expandability in obese subjects.     

Characterization and comparison of adipose tissue‐derived cells from human subcutaneous and omental adipose tissues

Different fat depots contribute differently to disease and function. These differences may be due to the regional variation in cell types and inherent properties of fat cell progenitors. To address the differences of cell types in the adipose tissue from different depots, the phenotypes of freshly isolated adipose tissue‐derived cells (ATDCs) from subcutaneous (SC) and omental (OM) adipose tissues were compared using flow cytometry. Our results showed that CD31^?CD34⁺CD45^?CD90^‐CD105^?CD146⁺ population, containing vascular smooth muscle cells and pericytes, was specifically defined in the SC adipose tissue while no such population was observed in OM adipose tissue. On the other hand, CD31^?CD34⁺CD45^?CD90^?CD105^?CD146^? population, which is an undefined cell population, were found solely in OM adipose tissue. Overall, the SC adipose tissue contained more ATDCs than OM adipose tissue, while OM adipose tissue contained more blood‐derived cells. Regarding to the inherent properties of fat cell progenitors from the two depots, adipose‐derived stem cells (ADSCs) from SC had higher capacity to differentiate into both adipogenic and osteogenic lineages than those from OM, regardless of that the proliferation rates of ADSCs from both depots were similar. The higher differentiation capacity of ADSCs from SC adipose tissue suggests that SC tissue is more suitable cell source for regenerative medicine than OM adipose tissue. Copyright © 2009 John Wiley & Sons, Ltd.     

Suppression of GATA-3 increases adipogenesis,reduces inflammation and improves insulin sensitivity in 3T3L-1 preadipocytes

Impaired adipogenesis plays an important role in the development of obesity-associated insulin resistance and type 2 diabetes. Adipose tissue inflammation is a crucial mediator of this process. GATA-3 plays important roles in adipogenesis and inflammation. The aim of this study is to investigate the impact of GATA-3 suppression on improving adipogenesis, lowering inflammation and reversing insulin resistance. GATA-3 levels were measured in subcutaneous (SC) and omental (OM) adipose tissues obtained from insulin sensitive (IS) and insulin resistant (IR) obese individuals during weight reduction surgeries. The effect of GATA-3 suppression on adipogenesis, expression of inflammatory cytokines and insulin resistance biomarkers was performed in 3T3L-1 mouse preadipocytes via transfection with GATA-3-specific DNAzyme. GATA-3 expression was higher in OM compared to SC adipose tissues and in stromal vascular fraction-derived differentiating preadipocytes from IR obese individuals compared to their IS counterparts. Suppression of GATA-3 expression in 3T3L-1 mouse preadipocytes with GATA-3 specific inhibitor reversed 4-hydroxynonenal-induced impaired adipogenesis and triggered changes in the expression of insulin signaling-related genes. GATA-3 inhibition also modulated the expression of IL-6 and IL-10 and lowered the expression of insulin resistance biomarkers (PAI-1 and resistin) and insulin resistance phosphoproteins (p-BAD, p-PTEN and p-GSK3β). Inhibiting GATA-3 improves adipocytes differentiation, modulates the secretion of inflammatory cytokines and improves insulin sensitivity in insulin resistant cells. Suppression of GATA-3 could be a promising tool to improve adipogenesis, restore insulin sensitivity and lower obesity-associated inflammation in insulin resistant individuals.     

Differences in Visceral Fat and Fat Bacterial Colonization between Ulcerative Colitis and Crohn’s Disease. An In Vivo and In Vitro Study

Crohn’s disease (CD) is notably characterized by the expansion of visceral fat with small adipocytes expressing a high proportion of anti-inflammatory genes. Conversely, visceral fat depots in ulcerative colitis (UC) patients have never been characterized. Our study aims were a) to compare adipocyte morphology and gene expression profile and bacterial translocation in omental (OM) and mesenteric (MES) adipose tissue of patients with UC and CD, and b) to investigate the effect of bacterial infection on adipocyte proliferation in vitro. Specimens of OM and MES were collected from 11 UC and 11 CD patients, processed and examined by light microscopy. Gene expression profiles were evaluated in adipocytes isolated from visceral adipose tissue using microarray and RTqPCR validations. Bacteria within adipose tissue were immuno-detected by confocal scanning laser microscopy. Adipocytes were incubated with Enterococcus faecalis and cells counted after 24h. Morphology and molecular profile of OM and MES revealed that UC adipose tissue is less inflamed than CD adipose tissue. Genes linked to inflammation, bacterial response, chemotaxis and angiogenesis were down-regulated in adipocytes from UC compared to CD, whereas genes related to metallothioneins, apoptosis pathways and growth factor binding were up-regulated. A dense perinuclear positivity for Enterococcus faecalis was detected in visceral adipocytes from CD, whereas positivity was weak in UC. In vitro bacterial infection was associated with a five-fold increase in the proliferation rate of OM preadipocytes. Compared to UC, visceral adipose tissue from CD is more inflamed and more colonized by intestinal bacteria, which increase adipocyte proliferation. The influence of bacteria stored within adipocytes on the clinical course of IBD warrants further investigations.     

Islet-1: a potentially important role for an islet cell gene in visceral fat

Objective: To examine differences in gene expression between visceral (VF) and subcutaneous fat (SF) to identity genes of potential importance in regulation of VF. Methods and Procedures: We compared gene expression (by DNA array and quantitative PCR (qPCR)) in paired VF and SF adipose biopsies from 36 subjects (age 54 ± 15 years, 15 men/21 women) with varying degrees of adiposity and insulin resistance, in chow and fat fed mice (± rosiglitazone treatment) and in c‐Cbl^?/? mice. Gene expression was also examined in 3T3‐L1 preadipocytes during differentiation. Results: A twofold difference or more was found between VF and SF in 1,343 probe sets, especially for genes related to development, cell differentiation, signal transduction, and receptor activity. Islet‐1 (ISL1), a LIM‐homeobox gene with important developmental and regulatory function in islet, neural, and cardiac tissue, not previously recognized in adipose tissue was virtually absent in SF but substantially expressed in VF. ISL1 expression correlated negatively with BMI (r = ?0.37, P = 0.03), abdominal fat (by dual energy X‐ray absorptiometry, r = ?0.44, P = 0.02), and positively with circulating adiponectin (r = 0.33, P = 0.04). In diet‐induced obese mice, expression was reduced in the presence or absence of rosiglitazone. Correspondingly, expression was increased in the c‐Cbl^?/? mouse, which is lean and insulin sensitive (IS). ISL1 expression was increased sevenfold in 3T3‐L1 preadipocytes during early (day 1) differentiation and was reduced by day 2 differentiation. Discussion: An important developmental and regulatory gene ISL1 is uniquely expressed in VF, probably in the preadipocyte. Our data suggest that ISL1 may be regulated by adiposity and its role in metabolic regulation merits further study.     

The FBXL10/KDM2B Scaffolding Protein Associates with Novel Polycomb Repressive Complex-1 to Regulate Adipogenesis

Polycomb repressive complex 1 (PRC1) plays an essential role in the epigenetic repression of gene expression during development and cellular differentiation via multiple effector mechanisms, including ubiquitination of H2A and chromatin compaction. However, whether it regulates the stepwise progression of adipogenesis is unknown. Here, we show that FBXL10/KDM2B is an anti-adipogenic factor that is up-regulated during the early phase of 3T3-L1 preadipocyte differentiation and in adipose tissue in a diet-induced model of obesity. Interestingly, inhibition of adipogenesis does not require the JmjC demethylase domain of FBXL10, but it does require the F-box and leucine-rich repeat domains, which we show recruit a noncanonical polycomb repressive complex 1 (PRC1) containing RING1B, SKP1, PCGF1, and BCOR. Knockdown of either RING1B or SKP1 prevented FBXL10-mediated repression of 3T3-L1 preadipocyte differentiation indicating that PRC1 formation mediates the inhibitory effect of FBXL10 on adipogenesis. Using ChIP-seq, we show that FBXL10 recruits RING1B to key specific genomic loci surrounding the key cell cycle and the adipogenic genes Cdk1, Uhrf1, Pparg1, and Pparg2 to repress adipogenesis. These results suggest that FBXL10 represses adipogenesis by targeting a noncanonical PRC1 complex to repress key genes (e.g. Pparg) that control conversion of pluripotent cells into the adipogenic lineage.     

The Effect of the Interleukin‐1 Cytokine Family Members IL‐1F6 and IL‐1F8 on Adipocyte Differentiation

Obesity is characterized by chronic low‐grade inflammation originating from expanding adipose tissue. In the present study, we examined the adipogenic expression levels of IL‐1F6 and IL‐1F8, both members of the IL‐1 family of cytokines, and their effects on adipose tissue gene expression. Although IL‐1F6 is primarily present in adipose tissue resident macrophages and induced by inflammation, IL‐1F8 is absent. IL‐1F6, but not IL‐1F8, reduces adipocyte differentiation, as shown by a significant decrease in PPARγ gene expression. Finally, both IL‐1F6 and IL‐1F8 are able to induce inflammatory gene expression in mature adipocytes. In conclusion, we demonstrate for the first time that IL‐1F6 is present in adipose tissue and that IL‐1F6 and IL‐1F8 are involved in the regulation of adipose tissue gene expression. Importantly, IL‐1F6 inhibits PPARγ expression which may lead to reduced adipocyte differentiation suggesting metabolic effects of this cytokine.     

Differential expression of plasminogen activator inhibitor-1, tumor necrosis factor-alpha,TNF-alpha converting enzyme and ADAMTS family members in murine fat territories

Our objective was to investigate expression of A disintegrin and metalloproteinase (ADAM) and ADAM proteins with a thrombospondin (TS) motif (ADAMTS) family members in adipose tissue of lean and obese mice. Five-week-old male mice were kept on standard chow (SFD) or on high fat diet (HFD) for 15 weeks, and subcutaneous (SC) and gonadal (GON) adipose tissue, as well as mature adipocytes and stromal-vascular (S-V) cells were harvested. mRNA levels of plasminogen activator inhibitor-1 (PAI-1), tumor necrosis factor-alpha (TNF-alpha), ADAM-17 (TACE or TNF-alpha converting enzyme), ADAMTS-1 and ADAMTS-8 were quantified in isolated adipose tissues and cell fractions, and during differentiation of murine preadipocytes. The HFD resulted in a significantly enhanced weight of isolated SC and GON fat pads, and in enhanced blood levels of glucose, cholesterol and PAI-1. ADAM-17, TNF-alpha, PAI-1, ADAMTS-1 and ADAMTS-8 mRNA were detected in both SC and GON adipose tissue of lean mice (SFD). In SC adipose tissue of obese mice (HFD), the expression of ADAM-17 and PAI-1 was enhanced and that of ADAMTS-1 reduced, whereas in GON adipose tissue expression of TNF-alpha was enhanced and that of ADAMTS-8 reduced. In lean and obese mice, expression of ADAM-17, ADAMTS-1 and ADAMTS-8 was higher in the S-V cell fraction than in mature adipocytes. During differentiation of murine 3T3-F442A preadipocytes, expression of ADAM-17 and ADAMTS-1 remained virtually unaltered, whereas that of ADAMTS-8 decreased as adipocytes matured. Several ADAM and ADAMTS family members are expressed in adipose tissue and during differentiation of preadipocytes. Modulation of their expression upon development of obesity is adipose tissue-dependent.     

Influence of obesity and insulin sensitivity on insulin signaling genes in human omental and subcutaneous adipose tissue

Obesity and insulin resistance are independent risk factors for metabolic syndrome, diabetes, and cardiovascular disease. Adipose tissue samples from nonobese (NO), insulin-sensitive obese (ISO), and insulin-resistant obese (IRO) subjects from subcutaneous (SC) and omental (OM) adipose tissue (n = 28) were analyzed by microarray and confirmed by real-time PCR. Insulin signaling gene expression changes were greater in OM than in SC tissue and were related to insulin resistance rather than to obesity; few genes correlated with body mass index. Insulin receptor and insulin receptor substrate 1 (IRS-1) increased in the IRO versus pooled insulin-sensitive (NO+ISO) subjects. In glucose transport, PI3Kalpha and PDK2 decreased in IRO subjects, whereas PI3Kgamma, Akt2, GLUT4, and GLUT1 increased. IRS-1 regulators Jnk and IKK increased in IRO (P < 0.01 and P < 0.001 respectively). In protein synthesis, most genes examined were downregulated in IRO subjects, including mTor, Rheb, and 4EBP and eIF members (all P < 0.05). In proliferation, SHC, SOS, and Raf1 (P < 0.05) were increased, whereas Ras and MEK1/2 kinase 1 (P < 0.05) were decreased, in IRO subjects. Finally, in differentiation, PPARgamma, CEBPalpha, and CEBPbeta decreased, whereas PPARdelta, CEBPgamma, and CEBPepsilon increased, in IRO subjects (P < 0.05). Together, microarray and real-time PCR data demonstrate that insulin resistance rather than obesity is associated with altered gene expression of insulin signaling genes, especially in OM adipose tissue.     

Depot-specific prostaglandin synthesis in human adipose tissue: a novel possible mechanism of adipogenesis

Despite the magnitude of the obesity epidemic, the mechanisms that contribute to increases in fat mass and to differences in fat depots are still poorly understood. Prostanoids have been proposed as potent adipogenic hormones, e.g. metabolites of prostaglandin J2 (PGJ2) bind and activate PPARγ. We hypothesize that an altered expression of enzymes in PGJ2 synthesis may represent a novel pathogenic mechanism in human obesity. We characterized adipose depot-specific expression of enzymes in PGJ2 synthesis, prostaglandin transporter and PPARγ isoforms. Paired omental and subcutaneous adipose tissue samples were obtained from 26 women undergoing elective abdominal surgery and gene expression examined in whole tissue and cultured preadipocytes using an Affymetrix cDNA microarray technique and validated with quantitative real-time PCR. All enzymes involved in prostaglandin synthesis were expressed in both adipose tissues. Expression of prostaglandin synthase-1 (PGHS1), prostaglandin D synthase (PTGDS), human prostaglandin transporter (hPGT) and PPARγ2 was higher in OM adipose tissue compared to SC, whereas 17β-hydroxysteroid dehydrogenase 5 (AKR1C3) showed predominance in SC adipose tissue. In SC adipose tissue, PGHS1 mRNA expression increased with BMI. The differential, depot-specific expression of key enzymes involved in transport, synthesis and metabolism of prostaglandins may have an important impact upon fat cell biology and may help to explain some of the observed depot-specific differences. In addition, the positive correlation between PGHS1 and BMI offers the novel hypothesis that the regulation of PG synthesis may have a role in determining fat distribution in human obesity.